The present invention relates to a food warmer, and more particularly, to an improved food warmer having closed loop heating control.
Food warmers are commercially used by restaurants, institutional kitchens, and fast food establishments for maintaining a variety of cooked food products, such as french fries, fish, potatoes, fried chicken, and the like, at a desired temperature. Food warmers typically use lamps with radiation in the visible and infrared spectrums, or radiant heaters with output in the infrared spectrum in combination with lamps which provide display lighting.
The food warmers may have an open loop control system which sets the output of the lamps and/or heaters to provide a temperature in the food warmer based on conditions found at the site, e.g., available voltage, airflow around the food warmer, and the geometry of the food warmer. Open loop control of radiant lamps is not desirable, since the lighting level in the food warmer and the color of food product contained in the food warmer is more strongly affected by control adjustment than the heat output, and is also more noticeable to the customer. Open loop control also does not take into account changes in the operating environment. Specifically, open loop control cannot compensate for voltage fluctuations which may occur as neighboring users go on an off line nor for air temperature fluctuations which may occur, for example, when a drive through window or doors of a restaurant are opened and closed.
Closed loop control has been difficult to implement in food warmers because different sensor types present various problems. Some sensors detect the air temperature as is done in an oven, however, heating in a food warmer is produced by radiation, not by hot air. Some sensors may sense the temperature of a portion of the food warmer itself, which receives and transmits heat differently than the food product. Other sensors use infrared heat detection to view the food product and then calculate the temperature. However, the emissivity used in such a calculation is different for the food product and the food warmer itself and the infrared detection device may at certain times view one or the other, or a combination of both, resulting in erroneous readings.
It is an object of the present invention to provide a closed loop heat control for a food warmer which reduces or wholly overcomes some or all of the aforesaid difficulties inherent in prior known devices. Particular objects and advantages of the invention will be apparent to those skilled in the art, that is, those who are knowledgeable or experienced in this field of technology, in view of the following disclosure of the invention and detailed description of certain preferred embodiments.
The principles of the invention may be used to advantage to provide a food warmer having closed loop heating control for more accurate control of a desired set point temperature.
In accordance with a first aspect, a heating control for a food warmer has a housing having a warming zone and a temperature sensor in the warming zone. The temperature sensor has a rate of heat absorption and a rate of heat loss substantially the same as a selected food product. A first heat source provides heat continuously to the warming zone. A second heat source provides heat to the warming zone in intermittent fashion to maintain a desired set point temperature of the warming zone, The heat required to maintain the warming zone at a desired temperature requires heat from both the first heat source and the second heat source.
In accordance with another aspect, a heating control for a food warmer has a housing having a warming zone and a temperature sensor in the warming zone. A light source warms and illuminates food product contained in the warming zone, and the light source is operated continuously while food product is in the warming zone. A radiant heater warms food product in the warming zone, and the heat required to maintain the food product at a desired temperature requires heat from both the light source and the radiant heater, A closed loop controller is responsive to a signal from the temperature sensor to control operation of the radiant heater to maintain a desired set point temperature of the warming zone.
In accordance with another aspect, a heating control for a food warmer has a housing having a hood and a base. The base has a warming zone and a temperature sensor is located in the warming zone. A plurality of lamps are secured to the hood to provide light and heat to food product contained in the warming, zone. The lamps are operated continuously while food product is in the warming zone. Each of a plurality of lamp reflectors is positioned adjacent a lamp to direct light and heat toward the warming zone. A radiant heater is secured to the hood to provide heat to warm the food product in the warming zone. The heat required to maintain the food product at a desired temperature requires heat from both the lamps and the radiant heater. A radiant heater reflector is adjacent the radiant heater to direct heat toward the warming, zone. A closed loop controller is responsive to a signal from the temperature sensor to control operation of the radiant heater to maintain a desired set point temperature of the warming zone.
In accordance with yet another aspect, a heating control for a food warmer has a housing having a warming zone. A temperature sensor in the warming zone has a rate of heat absorption and a rate of heat loss substantially the same as a selected food product. A radiant heater warms a food product in the warming zone. A closed loop controller is responsive to a signal from the temperature sensor to control operation of the radiant heater to maintain a desired set point temperature of the warming zone.
From the foregoing disclosure, it will be readily apparent to those skilled in the art, that is, those who are knowledgeable or experienced in this area of technology, that the present invention provides a significant technological advance. Preferred embodiments of the food warmer with closed loop heat control allow more accurate control of the temperature of food product contained in the food warmer, taking into account fluctuations in operating parameters and environmental conditions. These and additional features and advantages of the invention disclosed here will be further understood from the following detailed disclosure of certain preferred embodiments.